feedback about gears. stop doing it wrong! impedance.

Discussion in 'Sound Science' started by castleofargh, Dec 4, 2017.
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  1. headwhacker
    It is a form of EQ I agree. But it's like shooting in the dark EQ. Unless, measurements like you did is available then it's very difficult to predict how a headphone will behave. In my opinion even with the data available fixing the FR is messy on a high OI source than on a low OI source.
  2. SilverEars
    The thing is it's not always so straight forward. My Mojo is spec'd to have close to 0 output impedance, and my Andromeda outputs less bass than my Opus #2 which has 2ohm output impedance.

    Anyway what was posted by Castle has been known for a very long time(it's nothing new), and I saw iem loaded measurements from a guy that used to post here years ago(in which he deserves the credit!).
    Last edited: Dec 9, 2017
  3. castleofargh Contributor
    well it's called Ohm's law, not Argh's law so indeed I had nothing to do with it ^_^.
    the first guy who caught my attention doing RMAA tests with annoying IEMs to show some worst case impedance scenarios, was Markus Kraus using a UE triple.fi10. I doubt he was the first guy to ever consider that, but he was the first I saw put a list of gears for us to see measured. before him I hadn't yet fallen into the dark side of enjoying music so I can't say who first provided public intel on those stuff.

    and right now we have this topic that is still alive with a few members using other non flat impedance IEMs as load to estimate if the source is low impedance or not.
    it would be more direct to measure the impedance of the device, but the way they do it can also reveal protection caps, or maybe an amp section with a non flat impedance for some reason. so in a sense it's more interesting as a mean to know what to expect of the sound.
    also @HiFiChris bothered to make a tuto for those who wish to try stuff themselves so that's pretty cool. (guys just remember to check that you're not sending too loud a signal into your IEMs. with DAPs there is very little danger to break an IEM, but with stronger amps it could happen).

    as for your Mojo example, I'm not sure I get what you're trying to say, we're clearly missing some information here. is it related to this?
    or is it something else?
  4. SilverEars
    Why does it matter if it's in relation to what you as a specific example or not? I wrote about an experience(not what you'd expect) with Andromeda in regards to bass in relations to impedance outputs. Just trying to point out that you experience compared to what you'd expect can differ.
    Last edited: Dec 9, 2017
  5. castleofargh Contributor
    all right I got it. so to be clear for others. you must have meant
    I added the bold part.
    and well I'm not sure how headfi or SBAF would take me using their posts, so I advise people to google "Andromeda impedance" if they want to see an impedance graph ^_^. campfire gave 12.8ohm @1khz and Marv measured about 8ohm@1khz, so I don't know what's going on there, but I expect the general curve to be ok. anybody else measured the impedance of that IEM?
    the main point here is that the impedance of the Andromedia seems to rise in the upper frequencies, so we should get brighter sound(or less low end) on higher impedance sources. which goes with Marv's opinion and against what @SilverEars experienced.

    so how could we explain this?
    maybe your listening wasn't strict enough (volume matched?) and you got the wrong idea.
    maybe something else comes into play, other than basic ohm's law. we would need to see both sources measured to get maybe more clues about this.
    maybe the DAPs don't have a flat impedance response? I doubt it would be to the point of inverting the general direction of the signature, but it's not totally impossible I guess.
    maybe the Opus rolls off the low end for some reason (protective caps maybe?). do you get a lack of bass like a high pass filter got applied instead of just a little less overall low end?
    or maybe it's simply that at least one of the devices can't handle a load going too low? it's not like many devices are guaranteed to work great with stuff going below 8ohm. originally this wasn't supposed to happen on portable gears, but nowadays most TOTL IEMs go crazy low in impedance and don't seem to give a crap how hard that will be on the amp.

    in the end impedance ratios are just one aspect of more or less complicated designs. I used it on this topic to show how just that one aspect was already enough to get different signatures from the same IEM sometimes. or to get the wrong idea about a DAP or amp. I use impedance ratio to justify how people need to be careful when they make claims about the sound of a device if they discuss circumstances outside of their own listening conditions. I certainly didn't mean to say that the impedance ratio decides how everything will go. I wish it could be that simple. ^_^
  6. money4me247 Contributor
    @castleofargh, your first post was one of the most interesting and educational posts I've read in a long time! very fundamental point with great implications. well said.
  7. castleofargh Contributor
  8. stalepie
    are monitors better suited for higher output impedance sources, like in studio environment and for use with video cameras and other on-site equipment? Are they "expecting" the higher output impedance of older equipment to sound normal, and lower output impedance will actually make them sound thin or treble-focused?

    Why were they ever frequent? Was there some advantage to making them this way? was it easier and only until recently the output impedance was driven down low? I had the idea from somewhere that it became a lot more common to have low output impedance after the introduction of the iPod and then iPhone, but before that a lot of sources weren't so low. For instance, the Beyerdynamic A20 is 100 ohms, which breaks the 1/8th rule of their 600 ohm phones, and a senior Sony engineer that worked on the Wm1z Walkman said output impedance didn't matter when interviewed by Steven Rochlin.

    On this page it gives an answer for "Why 100ohm":

    1. It protects the A 20 from damage in the event of a short circuit on the headphone side.
    2. When using headphones that have different impedances one after the other, the jumps in volume level are much lower than if a very low output impedance was selected.
  9. castleofargh Contributor
    I'll let professionals answer those questions about if and why they used different standards and how things changed in the last decades(or not?). I don't have professional experience myself.
    but the purpose of a monitor being mainly a well balanced FR, if using a particular amp with a particular pair didn't result in flat response, it's fair to assume that professionals wouldn't use that combo. nowadays you can pretty much bypass that question by using powered monitors.

    what the designer of a specific pair of speakers had in mind as the source when he designed them? only him can tell. there are nowadays some expectations, but I have no idea how things were 60 years ago when basic tube designs were all the rage. I'm also guessing a wider adoption of negative feedback could have played a role as one of the potential benefits is lowered impedance. I'm really not the guy to ask all that, my audio history is very poor.

    I imagine when the trending portable gear was an ipod, it's fair to assume that many portable headphones and IEMs were at the very least tested to work fine with those sources. and as those ipods happened to have super weak output voltage and like 4ohm, maybe this factored in the final design of some gears? it certainly feels possible. not that it would always matter. not all headphones and IEMs have crazy impedance values or sensitivity.

    Sony is Sony. they'll tell you that the output impedance doesn't matter with a straight face. but they'll also talk about reducing the impedance of the battery cable as if it was a significant selling point(when did simply doing an ok job become a marketing argument?). and some years back, output impedance didn't matter so much that they ended up being unable to recommend some of their own DAPs to go with some of their IEMs. because the IEMs had that kind of impedance curve(it's the lower line for those who aren't familiar with this) :
    so I'd take those Sony interviews with a grain of salt. ^_^

    having a significant output impedance is said to be used by many as a way to protect the amp. maybe I'm wrong about that because I actually never bothered to check my assumptions, but I see it as making sure there is a load even in case of short circuit. so that the amp doesn't end up having to dissipate all the energy itself. any actual EE around to say if I'm full of crap with my idea of how that goes?
  10. 71 dB
    Flat impedance curve means that higher output impedance works fine.
    Tone controller/equaizer is better way to adjust thin sound that output impedance tweaking.

    Yes, easy and cheap. You just used the signal from speaker terminals and fed it through a resistor. The more powerful amp, the larger resistor they used! So, smaller less powerful amps had statistically lower output impedance and were better for heaphones, ironically.

    Yes, because portable devices have limited voltage/power, so you need low impedance levels to not waste the power on warming up resistors. You also want voltage-sensitive portable headphones which means low impedance too. Output impedance does matter unless you have completely flat impedance curve on your headphones.

    That's marketing BS, words to "justify" the not so optimal solution in respect of sound quality. The real reason is 100 Ω makes thing easier and cheaper. Some headphones may sound very nice driven from 100 Ω output, but for some other heaphones you need much lower output impedance.

    1. Opamps have internal protection so you don't need external protection measures.
    2. People should turn volume down/off when switching phones and never wear them before connection! :scream:
  11. castleofargh Contributor
    I updated the 2 variation graphs after noticing that I could make them slightly more accurate just from how I create the reference curve in REW. doesn't really change anything, it's just a tiny bit more accurate and makes the JH13 changes even more obviously aligned on the impedance curve.

    I tried to do the same for my HD650, but just the time I take to switch between gears, ends up being enough for the pads to give in a little and change the response almost as much as the impedance does. so I'm not showing those and the small bass bump on high impedance gears. maybe I'll do it without pads someday, but the 2 IEMs already show what's going on with impedance I think. so maybe I'll just stay lazy. ^_^
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